This invention relates to underreaming and chambering tools and more particularly to an arrangement for remotely indicating the position of movable cutter arms on the tool.
Rotary drills are commonly used for earth boring operations. Such drills are employed in oil and gas wells as well as in mining operations. Often it is desirable to enlarge the diameter of a hole drilled at some point a substantial distance below the surface. In oil and gas wells this is commonly referred to as underreaming, whereas in mining it is commonly referred to as chambering. For ease of explanation, both operations are generally referred to herein as underreaming.
To effect underreaming operations a variety of underreamers, hole openers, and the like have been devised. With some devices the underreamer can only be installed on the drill string when underreaming operations are taking place. This requires removal of the drill string each time a change is made from straight drilling to underreaming or vice versa.
Other devices employ various controllable cutter actuators to move underreaming cutters into or out of underreaming position while a drill is connected below the underreamer for drilling purposes. Some such devices use fluid pressure, for example, due to recirculating drilling mud or the like to actuate a cutter into an extended cutting or underreaming position. In other known underreaming devices, mechanical adjustment of the drill string connected to the underreamer and fluid or pneumatic pressure applied through the drill string is used to move cutters to the underreaming position. One such device is disclosed in U.S. Pat. No. 3,817,339.
Another underreamer which has a purely mechanical control is disclosed in copending patent application Ser. No. 668,412, filed Mar. 19, 1976 entitled "Underreamer Having Splined Torgue Transmitting Connector Between Telescoping Portions for Control of Cutter Position", now abandoned, A continuation of which was assigned Ser. No. 736,109 and was filed Oct. 27, 1976.
After an underreaming operation has been performed by an underreaming tool and the underreaming tool is removed from the hole, it is of extreme importance that the cutter arms be fully retracted to a non-cutting position in order to allow the underreaming tool to be removed from the hole without cutting away the smaller diameter hole above the underreamed portion. This is of extreme criticality in mining operations where the enlarged underreamed portion of the hole is to be used for blasting purposes. In this connection the enlarged diameter hole must be of limited length down hole in order to concentrate the explosive force down hole.
In one underreamer disclosed in copending patent application Ser. No. 668,557, filed Mar. 19, 1976, entitled UNDERREAMING TOOL WITH OVERRIDING EXTENDED ARM RETAINER, the cutter arms have an overridable means for holding them in an extended underreaming position. This allows the cutter arms to clean off any debris buildup as the underreamer is lifted up hole. When the smaller diameter hole above the underreamed area is reached, the smaller diameter hole engages the extended cutter arms, causing the overridable means to allow the arms to retract to a clearance position.
It has been found in underreaming tools using an overridable means for holding the cutter arms in the extended underreaming position that the cutter arms may remain extended due to restraining forces on the cutter arms created by debris buildup under the arms during the underreaming and drilling operations. As a result when the underreamer is removed from the hole the extended cutter arms will cut out the hole above the underreamed area. Thus it is desirable for the operator to known when the cutter arms do not properly retrack to a clearance position. However, it is difficult for the operator to determine the cutter arm position when the underreamer is remotely located down hole.